Compressive Strength of Concrete Cubes / Cylinders — Lab Manual

Objective & standard

Strength of hardened concrete at 7 and 28 days.

Standard: ASTM C39 / BS EN 12390-3

Apparatus

• Moulds 150 mm cubes or 150 × 300 mm cylinders
• Compression machine
• Curing tank
• Capping or grinding (cylinders)

Procedure

1. Cast the specimens in 2–3 layers with 25–35 tamps each; level the top.
2. Demould after 24 h and cure in water at 23 ± 2 °C.
3. Test at 7 and 28 days; wipe dry and measure the dimensions.
4. Load at 0.15–0.35 MPa/s (cylinders) until failure; note the failure type.
5. Average 2–3 specimens of the same age.

Calculations

• f = P ÷ A
• Cylinder ≈ 0.8 × cube strength
• 7-day strength ≈ 65–70 % of 28-day (OPC)

Typical values: 3000 psi (20.7 MPa) cylinders ≈ 26 MPa cubes. ACI 318 acceptance: average of 3 ≥ f′c and no test below f′c − 3.5 MPa.

Open the Compressive Strength calculator →

Data sheet (print this page)

Project: ____________________   Sample: __________   Date: __________   Tested by: __________

🖨 Print lab sheet